Gas compressor control device and gas turbine plant control mechanism

ABSTRACT

A gas compressor control device and a gas turbine plant control mechanism are disclosed. A fuel gas pressurized by a gas compressor is supplied to a gas turbine via fuel gas piping. A gas turbine control device adjusts the flow rate of the fuel gas into the gas turbine by exercising opening and closing control of a pressure control valve and a flow control valve. The gas compressor control device controls a fuel gas pressure at the outlet of the gas compressor by effecting opening and closing control of a recycle valve and an IGV. If load rejection or load loss occurs, the gas compressor control device opens the recycle valve in a preceding manner and closes the IGV in a preceding manner. Thus, elevation of the fuel gas pressure at the gas compressor outlet can be prevented, and elevation of a fuel gas pressure at an inlet of the gas turbine can be suppressed, thereby ensuring stable operation.

The entire disclosure of Japanese Patent Application No. 2002-265138filed on Sep. 11, 2002, including specification, claims, drawings andsummary, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a gas compressor control device and a gasturbine plant control mechanism, which are designed to be capable ofsuppressing a rise in the pressure of a fuel gas supplied to a gasturbine, even if load rejection or load loss occurs.

2. Description of the Related Art

In a gas turbine plant, as shown in FIG. 4, a gas turbine 2 forrotationally driving a generator 1 is supplied with a fuel gas from agas compressor 4 via fuel gas piping 3. That is, the fuel gas for use inthe gas turbine 2 is pressurized by the gas compressor 4 to a pressuresuitable for the gas turbine 2.

The amount of fuel consumed by the gas turbine 2 varies with a generatorload required of the gas turbine 2. In detail, when a gas turbinegenerator output increases, a fuel gas pressure P₂ at the inlet of thegas turbine lowers, so that the gas compressor 4 is further required toraise the pressure of the fuel gas. When the gas turbine generatoroutput decreases, on the other hand, the fuel gas pressure P₂ at the gasturbine inlet increases, so that the gas compressor 4 is required tolower the pressure of the fuel gas.

A conventional concrete control method for controlling the gas turbine 2and the gas compressor 4 will be described hereinafter.

As shown in FIG. 4, a pressure control valve 5 and a flow control valve6 are interposed in the fuel gas piping 3. The pressure control valve 5is disposed upstream (closer to the gas compressor 4), while the flowcontrol valve 6 is disposed downstream (closer to the gas turbine 2).

A gas turbine control device 10 controls the valve opening of the flowcontrol valve 6 (i.e. PID control) such that a deviation between anactual generator output W₁ and a preset target generator load set valueW₀ is zero. The gas turbine control device 10 also controls the valveopening of the pressure control valve 5 (i.e. PID control) such that adeviation between a flow control valve differential pressure ΔP₁, whichis the difference between the fuel gas pressure upstream from the flowcontrol valve 6 and the fuel gas pressure downstream from the flowcontrol valve 6, and a preset flow control valve differential pressureset value ΔP₀ is zero.

The gas compressor 4, on the other hand, is provided with a recycle pipe7 for returning the fuel gas from the gas compressor outlet to the gascompressor inlet, a recycle valve 8 interposed in the recycle pipe 7,and an IGV (inlet guide vane) 9 for controlling the amount of air takeninto the gas compressor 4.

A gas compressor control device 20 finds P₀-P₁, which is a deviationbetween a fuel gas pressure P₁ at the gas compressor outlet and a presetfuel gas supply pressure set value P₀. Using a control function FX₁ forthe recycle valve 8, the gas compressor control device 20 controls (PIDcontrol) the valve opening of the recycle valve 8 according to thedeviation P₀-P₁. Using a control function FX₂ for the IGV 9, moreover,the gas compressor control device 20 controls (PID control) the valveopening of the IGV 9 according to the deviation P₀-P₁.

Namely, the gas compressor control device 20 exercises control tooperate the IGV 9 and the recycle valve 8 of the gas compressor 4 sothat the fuel gas pressure P₁ at the gas compressor outlet is constant.Concretely, the gas compressor control device 20 controls the openingsin such a manner as to decrease the opening of the recycle valve 8 andincrease the opening of the IGV 9 when exercising control for raisingthe fuel gas pressure P₁, and to increase the opening of the recyclevalve 8 and decrease the opening of the IGV 9 when exercising controlfor lowering the fuel gas pressure P₁.

Generally, the gas turbine 2 and the gas compressor 4 are produced bydifferent manufacturers, and it has been common practice that the gasturbine 2 and the gas compressor 4 are not cooperatively controlled.

In gas turbine power generation equipment having a gas turbine and agenerator connected together, there has been a technique for exercisingpreceding control in order to prevent misfire or back fire of acombustor due to combustion instability (see, for example, JapaneseUnexamined Patent Publication No. 1994-241062).

If the load on the gas turbine 2 falls abruptly, namely, if loadrejection (main shut-off device open) occurs or load loss of the gasturbine occurs, the fuel gas pressure P₂ (P₁) at the gas turbine inlet(the gas compressor outlet) sharply increases. In this case,conventional simple one-loop feedback control over the pressure on thegas compressor 4, as shown in FIG. 4, is not enough to deal with thissharp increase. Thus, the fuel gas pressure P₂ (P₁) markedly rises, andthen lowers to the desired pressure.

As a result, differential pressure control of the gas turbine may failto accommodate such pressure changes, so that an excessive amount offuel is charged into the gas turbine 2, causing breakage to thecombustor or fuel oscillations.

Conventionally, therefore, a great distance has been provided betweenthe gas turbine 2 and the gas compressor 4 to lengthen the fuel gaspiping 3 and ensure a sufficiently large piping volume, therebyabsorbing the elevation of the fuel gas pressure due to a sudden loadfall (load rejection, load loss) of the gas turbine.

Recently, however, it has been required to construct a power plant in asmall premises area in pursuit of economy. With this restricted premisesarea, the conventional method of securing long piping between the gasturbine and the gas compressor is nearing its limits.

SUMMARY OF THE INVENTION

The present invention has been accomplished in the light of the earliertechnologies. Its object is to provide a gas compressor control deviceand a gas turbine plant control mechanism which are capable ofpreventing an excessive increase in a fuel gas pressure within fuel gaspiping during occurrence of a sudden load fall (load rejection or loadloss), even when the fuel gas piping connecting a gas turbine and a gascompressor together is short.

According to an aspect of the present invention for attaining the aboveobject, there is provided a gas compressor control device for exercisingopening control of a recycle valve interposed in a recycle pipe whichreturns a fuel gas from an outlet of a gas compressor to an inlet of thegas compressor, and opening control of an inlet guide vane provided inthe gas compressor,

the gas compressor control device comprising:

a computing capability unit for computing a recycle valve normal openingcommand (r₁) and an inlet guide vane normal opening command (i₁) basedon a deviation between a fuel gas pressure (P₁) at the gas compressoroutlet and a preset fuel gas supply pressure set value (P₀); and

a computing capability unit for computing a recycle valve precedingopening command (r₂) and an inlet guide vane preceding opening command(i₂) based on a deviation between an actual generator output (W₁), whichis an actual output of a generator rotationally driven by a gas turbinesupplied with the fuel gas from the gas compressor, and a first orderlag actual generator output (W₁′), which has been obtained by firstorder lag computation of the actual generator output (W₁), and

the gas compressor control device exercising;

during a normal operation, opening control of the recycle valve based ona value of the recycle valve normal opening command (r₁), and openingcontrol of the inlet guide vane based on a value of the inlet guide vanenormal opening command (i₁); and

in an event of a sudden load fall, opening control of the recycle valvebased on a value obtained by adding the recycle valve preceding openingcommand (r₂) to the recycle valve normal opening command (r₁), andopening control of the inlet guide vane based on a value obtained byadding the inlet guide vane preceding opening command (i₂) to the inletguide vane normal opening command (i₁).

Because of the above-described features, in the event of load loss orload rejection, the recycle valve can be opened in a preceding manner,and the inlet guide vane (IGV) can be closed in a preceding manner. As aresult, the fuel gas pressure at the gas compressor outlet can belowered to suppress the elevation of the fuel gas pressure at the gasturbine inlet. Thus, stable operation can be performed.

According to another aspect of the present invention, there is provideda gas turbine plant control mechanism comprising:

a gas compressor control device for exercising opening control of arecycle valve interposed in a recycle pipe which returns a fuel gas froman outlet of a gas compressor to an inlet of the gas compressor, andopening control of an inlet guide vane provided in the gas compressor;and

a gas turbine control device for exercising opening control of apressure control valve and a flow control valve interposed in gas pipingwhich feeds the fuel gas from the gas compressor to a gas turbine, andwherein:

the gas turbine control device comprises a capability unit for feedingan actual generator output (W₁), which is an actual output of agenerator rotationally driven by the gas turbine, to the gas compressorcontrol device, and for feeding a load sudden fall signal to the gascompressor control device for a preset period of time when load loss orload rejection occurs; and

the gas compressor control device comprises:

a computing capability unit for computing a recycle valve normal openingcommand (r₁) and an inlet guide vane normal opening command (i₁) basedon a deviation between a fuel gas pressure (P₁) at the gas compressoroutlet and a preset fuel gas supply pressure set value (P₀); and

a computing capability unit for computing a recycle valve precedingopening command (r₂) and an inlet guide vane preceding opening command(i₂) based on a deviation between the actual generator output (W₁),which is the actual output of the generator, and a first order lagactual generator output (W₁′), which has been obtained by first orderlag computation of the actual generator output (W₁), and

the gas compressor control device exercises;

when the load sudden fall signal has not been entered, opening controlof the recycle valve based on a value of the recycle valve normalopening command (r₁), and opening control of the inlet guide vane basedon a value of the inlet guide vane normal opening command (i₁); and

when the load sudden fall signal has been entered, opening control ofthe recycle valve based on a value obtained by adding the recycle valvepreceding opening command (r₂) to the recycle valve normal openingcommand (r₁), and opening control of the inlet guide vane based on avalue obtained by adding the inlet guide vane preceding opening command(i₂) to the inlet guide vane normal opening command (i₁).

Because of the above-described cooperative control by the gas turbinecontrol device and the gas compressor control device, in the event ofload loss or load rejection, the recycle valve can be opened in apreceding manner, and the inlet guide vane (IGV) can be closed in apreceding manner. As a result, the fuel gas pressure at the gascompressor outlet can be lowered to suppress the elevation of the fuelgas pressure at the gas turbine inlet. Thus, stable operation can beperformed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a block configurational drawing showing a gas turbine plantincorporating control devices and a control mechanism according to thepresent invention;

FIG. 2 is a block diagram showing the dynamic characteristics of the gasturbine plant in the event of load rejection or load loss;

FIG. 3 is a simplified block diagram showing the dynamic characteristicsof the gas turbine plant in the event of load rejection or load loss;and

FIG. 4 is a block configurational drawing showing a gas turbine plantincorporating a conventional control device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments and actions of the present invention will now bedescribed with reference to the accompanying drawings, which in no waylimit the invention.

In the present invention, signals of actual generator output,parallel-off and sudden load fall (sudden fall in generator output) arefed from a gas turbine control device to a gas compressor controldevice. If load rejection or load loss occurs in a gas turbine, the gascompressor control device actuates an IGV and a recycle valve of a gascompressor in a preceding manner to prevent a rise in the fuel gaspressure at the inlet of the gas turbine.

The following Bernoulli's equation (1) holds between a fuel gas flowvelocity V₁ and a fuel gas pressure P₁ at the outlet of the gascompressor and a fuel gas flow velocity V₂ and a fuel gas pressure P₂ atthe inlet of the gas turbine. From this Bernoulli's equation (1),equation (2) is derived. $\begin{matrix}{{\frac{V_{1}^{2}}{2g} + \frac{P_{1}}{\gamma}} = {\frac{V_{2}^{2}}{2g} + \frac{P_{2}}{\gamma}}} & (1)\end{matrix}$where

-   -   V₁: fuel gas flow velocity (m/s) at gas compressor outlet,    -   V₂: fuel gas flow velocity (m/s) at gas turbine inlet,    -   P₁: fuel gas pressure (kg/m²) at gas compressor outlet,    -   P₂: fuel gas pressure (kg/m²) at gas turbine inlet, and    -   γ: gas turbine fuel specific gravity (kg/m³) $\begin{matrix}        {P_{1} = {P_{2} - {\left( {V_{1}^{2} - V_{2}^{2}} \right) \times \frac{\gamma}{2g}}}} & (2)        \end{matrix}$

Furthermore, the following relation (3) statically holds between theflow velocity V of the fuel gas consumed by the gas turbine and agenerator output MW.V=f(MW)/A  (3)where

-   -   MW: gas turbine generator output (actual generator load) (MW),        and    -   A: sectional area of piping

That is, if load rejection or load loss occurs, the fuel gas flowvelocity (fuel consumption) V₂ at the gas turbine inlet lowers. If thefuel gas pressure P₁ and the fuel gas flow velocity (discharge) V₁ atthe gas compressor outlet do not vary at this time, the fuel gaspressure P₂ at the gas turbine inlet increases.

After the fuel gas pressure P₂ at the gas turbine inlet increases, thefuel gas flow velocity (fuel gas flow rate) V₁ at the gas compressoroutlet follows the fuel gas flow velocity (fuel consumption) V₂ at thegas turbine inlet, so that V₁=V₂, whereupon the fuel gas pressure P₁ atthe gas compressor outlet also increases.

Finally, the fuel gas pressure is controlled to a prescribed value byfuel gas pressure control at the gas turbine inlet and fuel gas pressurecontrol at the gas compressor outlet. Thus, both of the fuel gaspressures P₁ and P₂ return to their prescribed values and settle. Bythen, the fuel gas pressure P₂ at the gas turbine inlet fluctuates,causing abnormality to combustion in the gas turbine, generatingcombustion oscillations.

If the fuel gas piping between the gas turbine and the gas compressor islong, it takes time until V₁=V₂. The fuel gas pressure at the gascompressor outlet minimally fluctuates. Thus, the fuel gas pressure P₂at the gas turbine inlet returns to the prescribed value early, and canminimize influence on gas turbine combustion. Hence, the fuel gas pipinghas hither to been made long.

However, the aforementioned phenomenon—the elevation of the fuel gaspressure P₂ at the gas turbine inlet in the event of load rejection orload loss—can be suppressed, even if the fuel gas piping between the gasturbine and the gas compressor is short, by exercising control such asto lower the fuel gas pressure P₁ at the gas compressor outlet in apreceding manner.

The dynamic characteristics in the event of load rejection or load lossare expressed as shown in FIG. 2 by use of a block diagram. In FIG. 2,T₁ represents a delay time from the supply of fuel to the gas turbineuntil the reflection of the fuel supply in the output of the gasturbine, and T₂ represents the time from a change in the fuel flowvelocity at the gas turbine inlet until the fuel flow velocity change isreflected in the fuel flow velocity at the gas compressor outlet.

In the block diagram of FIG. 2, if the fuel gas piping between the gasturbine and the gas compressor is long, the delay time T₂ increases. Asa result, the result of calculation of V₁ ²-V₂ ² in the event of loadrejection or load loss takes a large negative value. Thus, even when thefuel gas pressure P₂ at the gas turbine inlet takes a large value, thefuel gas pressure P₁ at the gas compressor outlet is not very high.

Finally, V₁=V₂, and the fuel gas pressure P₁ at the gas compressoroutlet equals the fuel gas pressure P₂ at the gas turbine inlet.

The block diagram shown in FIG. 2 can be simplified as shown in theblock diagram of FIG. 3.

Before load rejection or load loss occurs, the fuel gas pressure P₁ atthe gas compressor outlet equals the fuel gas pressure P₂ at the gasturbine inlet. Thus, in case of load rejection or load loss, it is foundthat the elevation of the fuel gas pressure at the gas compressor outletdepends on the value of the actual generator output before theoccurrence of load rejection or load loss, or depends on how fast theactual generator output fell.

EXAMPLE

Next, an example for embodying the present invention will be describedwith reference to FIG. 1. Portions exhibiting the same capabilities asin the earlier technology shown in FIG. 4 are assigned the samenumerals, and descriptions of these portions will be offered briefly.

As shown in FIG. 1, a gas compressor 4 is provided with a recycle pipe7, a recycle valve 8, and an IGV (inlet guide vane) 9. A pressurecontrol valve 5 and a flow control valve 6 are interposed in fuel gaspiping 3A. A fuel gas, increased in pressure by the gas compressor 4, ispassed through the fuel gas piping 3A and supplied to a gas turbine 2.The gas turbine 2 supplied with the fuel gas rotationally drives agenerator 1 to generate electric power.

The fuel gas piping 3A is shorter than the conventional fuel gas piping3. Except that the fuel gas piping 3A is shorter, the above-mentionedmechanical layout and configuration are the same as in the earliertechnology (see FIG. 4).

A gas turbine control device 100 controls the valve opening of the flowcontrol valve 6 (i.e. PID control) such that a deviation between anactual generator output W₁ and a preset target generator load set valueW₀ is zero. The gas turbine control device 100 also controls the valveopening of the pressure control valve 5 (i.e. PID control) such that adeviation between a flow control valve differential pressure ΔP₁, whichis the difference between the fuel gas pressure upstream from the flowcontrol valve 6 and the fuel gas pressure downstream from the flowcontrol valve 6, and a preset flow control valve differential pressureset value ΔP₀ is zero. These control capabilities are the same as thoseof the conventional gas turbine control device 10 (see FIG. 4).

In the present embodiment, moreover, the gas turbine control device 100has the following new capabilities (1) and (2) which the earliertechnology lacks:

(1) The capability of sending a load sudden fall signal SW, a one shotpulse, to a gas compressor control device 200 over a preset period, whena sudden fall in load, i.e. at least one of load loss and loadrejection, occurs. In this case, the period for which the load suddenfall signal SW is outputted (the period for which the one shot pulse isat a high level) is the period between the occurrence of load loss orload rejection and the settlement of fuel gas pressures P₁, P₂ atprescribed values. This period is set for each plant.(2) The capability of sending the actual generator output W₁ to the gascompressor control device 200.

The gas compressor control device 200 has the capability of controllingthe valve openings of the recycle valve 8 and the IGV 9, and exercisescontrol in manners which are different between normal operation (anoperation in the absence of load loss or load rejection) and theoccurrence of load loss or load rejection.

First, the respective computing capabilities of the gas compressorcontrol device 200 will be described. Then, the manners of controlduring normal operation and in the event of a sudden load fall (loadloss or load rejection) will be explained.

The deviation computing capability 201 of the gas compressor controldevice 200 finds a fuel gas pressure deviation P₁-P₀, which is adeviation between the fuel gas pressure P₁ at the gas compressor outletand a preset fuel gas supply pressure set value P₀.

A PID control capability 202 finds a recycle valve normal openingcommand r₁ based on the fuel gas pressure deviation P₁-P₀, while a PIDcontrol capability 203 finds an IGV normal opening command i₁ based onthe fuel gas pressure deviation P₁-P₀.

An adding capability 204 adds the recycle valve normal opening commandr₁ and a recycle valve preceding opening command r₂ (to be describedlater) to find a recycle valve command r₃. Whereas an adding capability205 adds the IGV normal opening command i₁ and an IGV preceding openingcommand i₂ (to be described later) to find an IGV command i₃.

A recycle valve control function capability (Fx₁) 206 finds a recyclevalve opening control signal R of a value corresponding to the recyclevalve command r₃, and opening control of the recycle valve 8 is effectedresponsive to the value of the recycle valve opening control signal R.Whereas an IGV control function capability (Fx₂) 207 finds an IGVopening control signal I of a value corresponding to the IGV command i₃,and opening control of the IGV 9 is effected responsive to the value ofthe IGV opening control signal I.

A first order lag function capability 208 outputs the actual generatoroutput W₁, unchanged, during the period of time that the load suddenfall signal SW has not been entered, and outputs a first order lagactual generator output W₁′, which has been obtained by first order lagcomputation of the actual generator output W₁, during the period of timethat the load sudden fall signal SW has been entered.

A deviation computing capability 209 finds an actual generator outputdeviation W₁′-W₁, which is a deviation between the first order lagactual generator output W₁′ and the actual generator output W₁.

A recycle valve preceding control function capability (Fx₄) 210 findsthe recycle valve preceding opening command r₂ based on the actualgenerator output deviation W₁′-W₁. An IGV preceding control functioncapability (Fx₃) 211 finds an IGV preceding opening command i₂ based onthe actual generator output deviation W₁′-W₁.

When the load sudden fall signal SW has not been entered, the output ofthe deviation computing capability 209 is zero, so that the recyclevalve preceding opening command r₂ and the IGV preceding opening commandi₂ are also zero. When the load sudden fall signal SW has been entered,the deviation between the first order lag actual generator output W₁′and the actual generator output W₁ increases. As a result, the recyclevalve preceding opening command r₂ and the IGV preceding opening commandi₂ are outputted which take command values corresponding to the value ofthe actual generator output deviation W₁′-W₁ outputted by the deviationcomputing capability 209.

With the gas compressor control device 200 having the abovecapabilities, the recycle valve preceding opening command r₂ is zero innormal times. Thus, the recycle valve command r₃=the recycle valvenormal opening command r₁. Consequently, the recycle valve controlfunction capability 206 finds the recycle valve opening control signal Rof a value corresponding to the recycle valve command r₃ (=r₁).Responsive to the value of the recycle valve opening control signal R,opening control of the recycle valve 8 is exercised.

In normal times, the IGV preceding opening command i₂ is zero. Thus, theIGV command i₃=the IGV normal opening command i₁. Consequently, the IGVcontrol function capability 207 finds the IGV opening control signal Iof a value corresponding to the IGV command i₃ (=i₁). Responsive to thevalue of the IGV opening control signal I, opening control of the IGV 9is exercised.

As a result, when the fuel gas pressure P₁ is high, the valve opening ofthe recycle valve 8 is great, while the opening of the IGV is small.When the fuel gas pressure P₁ is low, the valve opening of the recyclevalve 8 is small, while the opening of the IGV is great.

With the gas compressor control device 200 having the abovecapabilities, the recycle valve preceding opening command r₂ takes somevalue in the event of load loss or load rejection. Thus, the recyclevalve command r₃=the recycle valve normal opening command r₁+the recyclevalve preceding opening command r₂. Consequently, the recycle valvecontrol function capability 206 finds the recycle valve opening controlsignal R of a value corresponding to the recycle valve command r₃(=r₁+r₂). Responsive to the value of the recycle valve opening controlsignal R, opening control of the recycle valve 8 is exercised.

In the event of load loss or load rejection, the IGV preceding openingcommand i₂ takes some value. Thus, the IGV command i₃=the IGV normalopening command i₁+the IGV preceding opening command i₂. Consequently,the IGV control function capability 207 finds the IGV opening controlsignal I of a value corresponding to the IGV command i₃ (=i₁+i₂).Responsive to the value of the IGV opening control signal I, openingcontrol of the IGV 9 is exercised.

As a result, in the event of load loss or load rejection, the recyclevalve 8 can be opened in a preceding manner, while the IGV can be closedin a preceding manner. By so doing, the fuel gas pressure P₁ at the gascompressor outlet can be lowered, and the increase in the fuel gaspressure P₂ at the gas turbine inlet can be suppressed.

Because of the above-described control, even with the short fuel gaspiping 3A, the fuel gas pressures P₁, P₂ can be prevented fromincreasing excessively, and breakage of the combustor or the occurrenceof combustion oscillations can be prevented, in the event of load lossor load rejection. Thus, stable operation can be ensured.

Actually, when load rejection or load loss occurs, it suffices tosuppress a rise in the fuel gas pressure P₂ at the gas turbine inlet.Hence, the functions Fx₃, Fx₄ used by the preceding control functioncapabilities 210, 211 shown in FIG. 1 are not fed the values obtainedstrictly by the calculations shown in the block diagrams of FIGS. 2 and3, but are initially supplied with values sufficiently smaller than thevalues given by the calculations. Then, the values supplied are adjustedin accordance with changes in the fuel gas pressure P₂ at the gasturbine inlet during load fluctuations.

The time constant T₂, used in the first order lag function capability208, is also determined by actually operating the plant, and observing adelay in changes in the fuel gas pressure P₁ at the gas compressoroutlet in response to changes in the fuel gas pressure P₂ at the gasturbine inlet.

While the present invention has been described in the foregoing fashion,it is to be understood that the invention is not limited thereby, butmay be varied in many other ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the appended claims.

1. A gas compressor control device for exercising opening control of arecycle valve interposed in a recycle pipe which returns a fuel gas froman outlet of a gas compressor to an inlet of said gas compressor, andopening control of an inlet guide vane provided in said gas compressor,said gas compressor control device comprising: a computing capabilityunit for computing a recycle valve normal opening command (r₁) and aninlet guide vane normal opening command (i₁) based on a deviationbetween a fuel gas pressure (P₁) at said gas compressor outlet and apreset fuel gas supply pressure set value (P₀); and a computingcapability unit for computing a recycle valve preceding opening command(r₂) and an inlet guide vane preceding opening command (i₂) based on adeviation between an actual generator output (W₁), which is an actualoutput of a generator rotationally driven by a gas turbine supplied withthe fuel gas from said gas compressor, and a first order lag actualgenerator output (W₁′), which has been obtained by first order lagcomputation of said actual generator output (W₁), and said gascompressor control device exercising: during a normal operation, openingcontrol of said recycle valve based on a value of said recycle valvenormal opening command (r₁), and opening control of said inlet guidevane based on a value of said inlet guide vane normal opening command(i₁); and in an event of a sudden load fall, opening control of saidrecycle valve based on a value obtained by adding said recycle valvepreceding opening command (r₂) to said recycle valve normal openingcommand (r₁), and opening control of said inlet guide vane based on avalue obtained by adding said inlet guide vane preceding opening command(i₂) to said inlet guide vane normal opening command (i₁).
 2. A gasturbine plant control mechanism comprising: a gas compressor controldevice for exercising opening control of a recycle valve interposed in arecycle pipe which returns a fuel gas from an outlet of a gas compressorto an inlet of said gas compressor, and opening control of an inletguide vane provided in said gas compressor; and a gas turbine controldevice for exercising opening control of a pressure control valve and aflow control valve interposed in gas piping which feeds the fuel gasfrom said gas compressor to a gas turbine, and wherein: said gas turbinecontrol device comprises a capability unit for feeding an actualgenerator output (W₁), which is an actual output of a generatorrotationally driven by said gas turbine, to said gas compressor controldevice, and for feeding a load sudden fall signal to said gas compressorcontrol device for a preset period of time when load loss or loadrejection occurs; and said gas compressor control device comprises: acomputing capability unit for computing a recycle valve normal openingcommand (r₁) and an inlet guide vane normal opening command (i₁) basedon a deviation between a fuel gas pressure (P₁) at said gas compressoroutlet and a preset fuel gas supply pressure set value (P₀); and acomputing capability unit for computing a recycle valve precedingopening command (r₂) and an inlet guide vane preceding opening command(i₂) based on a deviation between said actual generator output (W₁),which is the actual output of said generator, and a first order lagactual generator output (W₁′), which has been obtained by first orderlag computation of said actual generator output (W₁), and said gascompressor control device exercises: when said load sudden fall signalhas not been entered, opening control of said recycle valve based on avalue of said recycle valve normal opening command (r₁), and openingcontrol of said inlet guide vane based on a value of said inlet guidevane normal opening command (i₁); and when said load sudden fall signalhas been entered, opening control of said recycle valve based on a valueobtained by adding said recycle valve preceding opening command (r₂) tosaid recycle valve normal opening command (r₁), and opening control ofsaid inlet guide vane based on a value obtained by adding said inletguide vane preceding opening command (i₂) to said inlet guide vanenormal opening command (i₁).